Conventional steering control linkage housings are fabricated by casting of molten aluminum or other materials. A valve housing comprised generally of cast iron is also used in the case of power steering. The fabrication of such components is attended by various problems. Complex and precise procedures are required for assembly and alignment of a cast iron valve housing with a cast aluminum steering control linkage housing, to ensure correct skew angular positioning of the components of the steering control linkage.
One reason why it is difficult to achieve proper alignment of conventional steering control linkage housings comprised of cast material is that there are two subassemblies which must be aligned:
the rack and its housing, and PA1 the pinion, the valve system, and their housings. PA1 on the distal end of the steering column shaft (pinion shaft) which projects beyond the pinion, which pinion is a cylindrical pinion having helicoidal dentation, and PA1 radially outwardly of the support bearing which supports said shaft and is mounted in the steering control linkage housing element which is angularly disposed (in a skew angular relation) with respect to the conventional housing element which houses the rack.
The parts of the housing must be in correct skew angular alignment in order to achieve good operating characteristics of the steering system, and particularly the steering control linkage.
The alignment procedures may require different skew angular alignments depending on the particular variant of the steering system used, and necessitate the use of different casting molds for fabricating the elements of the steering control linkage housings and for adapting the power-assisted steering valve housing. For each situation, a specific skew angular alignment of the steering column shaft (pinion shaft) and the rack housing is required, in order for the steering system to function properly.
Another problem which occurs with steering systems is the undesirable noise generated by excessive frictional play between the dentation of the pinion and the dentation of the rack. Such noise is a problem in power-assisted steering systems as well as manual systems. In some cases, the vibration is absorbed by elasticity in the steering system. Otherwise it must be reduced to acceptable limits in order to avoid noise which is disagreeable to the driver and which signals improper functioning of the engaged components.
This noise problem may be due to incorrect alignment of the contoured openings in the housing, but the main cause of steering system noise is axial stresses in the joints between the housing and the chassis, which stresses give rise to a force component perpendicular to the rack bar and tending to distance the rack bar from the pinion, thereby acting counter to the means integrated in the steering assembly which are intended to regulate the relative positions of the rack and pinion.
The said axial stresses also act axially on the rack, which rack is generally mounted with releasable support means on an end bearing in the steering control linkage housing, wherewith in addition to the component of said stresses which act perpendicularly to the rack, the axial stresses give rise to an undesirable axial movement of the rack which interferes with correct interengagement of the rack and the pinion, again tending to cause the respective dentations to separate, wherewith when, in alleviation of this separation, the rack tends to return to its initial position. The result is noise, in an intensity and frequency which depend exclusively on the intensity of the abovementioned axial stresses.
The conventional means used by automobile manufacturers to address these drawbacks in steering control linkages is to use high precision molds for fabricating the housings, in order to achieve the correct alignment of the steering control linkage components. The concept is that substantial improvement in operation will result from improvements in such alignment. In addition, the known technique of providing devices which periodically regulate the position of the rack bar has been used. The general such device comprises a manually adjustable thrust bearing which is elastically urged counter to the direction of the axial stresses. These devices function well, but when over-adjusted (which is always a possibility) the result is that the rack bar is not properly re-engaged, which is detrimental to the mechanism because the re-engagement force is too great or too small, either momentarily (dynamically) or on a sustained basis.